Efforts have been made to reduce emissions in the exhaust gas produced by internal combustion engines. One of the components in the exhaust system for a vehicle used for reducing emissions is an exhaust catalyst. One type of catalyst is referred to as a “three-way catalyst.” A three-way catalyst performs three different conversions of various exhaust emissions. One type of conversion is the reduction of nitrogen oxides to nitrogen and oxygen, another type of conversion is the oxidation of carbon monoxide to carbon dioxide, and the third conversion is the oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water.
A catalyst is most effective at controlling exhaust emissions when the catalyst is at the desired target threshold temperature, or “light-off” temperature. However, when engine ignition first occurs, the engine produces the highest amount of emissions, and the catalyst is typically at ambient temperature (or some other temperature which is well below light-off temperature), such that the catalyst is less effective at reducing emissions just after engine ignition.
Many attempts have been made to improve the efficiency of the catalyst. One of these past solutions has been to increase the rate at which the temperature of the catalyst increases. Another solution has included using the engine exhaust gas to provide heat to increase the temperature of the catalyst.
Some existing solutions incorporate the use of engine exhaust gas as part of the formula to create heat in the catalyst bed. One of the drawbacks to these strategies is that the catalyst is below the “light-off” temperature, where conversion of emissions is greatest, resulting in poor emissions during the initial period.
Accordingly, there exists a need for proactive heating of the catalyst, such that the catalyst is at light-off temperature prior to engine ignition.